A Novel Molecular Weight Jump Reaction of Polybutadiene Catalysed by Nickel

Abstract

A novel reaction of polybutadiene with vinyl substituted aromatic hydrocarbons, e. g., styrene and bromine compound, e. g., t-butyl bromide, was studied at 120-460°C under the condition of unquenched state of nickel catalyst after polymerization of butadiene. The polybutadiene was obtained by using nickel organic compound/boron trifluoride etherate/trialkylaluminum catalyst system. This reaction brings about an increase in molecular weight and in Mooney viscosity of polybutadiene and is called “Molecular weight jump reaction”.
The mode of the reaction varies with the concentration of nickel catalyst, vinyl substituted aromatic hydrocarbon and bromine compound as well as reaction temperature and the reaction does not occur when any of the above substances is not present. If a compound of chlorine or iodine is used instead of that of bromine, the reaction does not occur or gives a gelled polymer. When butadiene monomer is present, the reaction is retarded.
The resulting products, having Mooney viscosity by a factor of about two or three than that of the starting polybutadiene, are consist of almost linear polybutadienes containing trace or small amount of vinyl substituted aromatic hydrocarbon unit, give no gel and are suitable for industrial material after oil extending.
As is shown in the molecular weight distribution curve, the resulting products has wider high molecular weight region than that of the starting polybutadiene and the heterogeneous jump reaction in this high molecular weight region might presumably occur.
It was also assumed that the reaction proceeded in terms of radical coupling of styryl radicals attached to the ends of polybutadiene catalysed by active nickel.